Re: [Qemu-devel] [PATCH for-2.1 2/2] acpi: mark ACPI tables ROM blob as extend-able on migration

[Dr. David Alan Gilbert]

* Igor Mammedov (address@hidden) wrote:
> It fixes migration failure for machine type pc-i440fx-1.7 from
> QEMU 1.7/2.0 to QEMU 2.1
> 
> Migration fails due to ACPI tables size grows across 1.7-2.1
> versions. That causes ACPI tables ROM blob to change its size
> differently for the same configurations on different QEMU versions.
> As result migration code bails out when attempting to load
> smaller ROM blob into a bigger one on a newer QEMU.
> To trigger failure it's enough to add pci-bridge device to QEMU CLI
>
> Marking ACPI tables ROM blob as extend-able on migration allows
> QEMU to load smaller ACPI tables from QEMU 1.7/2.0, fixing
> forward migration failure introduced since 2.0 which affects
> only configurations that cause ACPI ROM blob size change.

(To follow up from an irc thread earlier today)
I only vaguely understand this case but my understanding is:

  1) It's a block of data that's never mapped into the guests address
space
  2) It can change, but only at guest reset
  3) Worst case is it can get upto about 2MB in size

it's pretty marginal whether this thing should be a RAMBlock,
it doesn't feel like normal RAM or ROM in most ways; but there
again 2MB is getting a bit large for the device state; hmm.

Dave

> 
> Signed-off-by: Igor Mammedov <address@hidden>
> ---
>  hw/core/loader.c     | 6 +++++-
>  hw/i386/acpi-build.c | 2 +-
>  include/hw/loader.h  | 5 +++--
>  3 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/core/loader.c b/hw/core/loader.c
> index 2bf6b8f..d09b894 100644
> --- a/hw/core/loader.c
> +++ b/hw/core/loader.c
> @@ -722,7 +722,8 @@ err:
>  
>  void *rom_add_blob(const char *name, const void *blob, size_t len,
>                     hwaddr addr, const char *fw_file_name,
> -                   FWCfgReadCallback fw_callback, void *callback_opaque)
> +                   FWCfgReadCallback fw_callback, void *callback_opaque,
> +                   bool extendable)
>  {
>      Rom *rom;
>      void *data = NULL;
> @@ -742,6 +743,9 @@ void *rom_add_blob(const char *name, const void *blob, 
> size_t len,
>  
>          if (rom_file_has_mr) {
>              data = rom_set_mr(rom, OBJECT(fw_cfg), devpath);
> +            if (extendable) {
> +                memory_region_permit_extendable_migration(rom->mr);
> +            }
>          } else {
>              data = rom->data;
>          }
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index ebc5f03..651c06b 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -1558,7 +1558,7 @@ static void *acpi_add_rom_blob(AcpiBuildState 
> *build_state, GArray *blob,
>                                 const char *name)
>  {
>      return rom_add_blob(name, blob->data, acpi_data_len(blob), -1, name,
> -                        acpi_build_update, build_state);
> +                        acpi_build_update, build_state, true);
>  }
>  
>  static const VMStateDescription vmstate_acpi_build = {
> diff --git a/include/hw/loader.h b/include/hw/loader.h
> index 796cbf9..e5a24ac 100644
> --- a/include/hw/loader.h
> +++ b/include/hw/loader.h
> @@ -57,7 +57,8 @@ int rom_add_file(const char *file, const char *fw_dir,
>                   bool option_rom);
>  void *rom_add_blob(const char *name, const void *blob, size_t len,
>                     hwaddr addr, const char *fw_file_name,
> -                   FWCfgReadCallback fw_callback, void *callback_opaque);
> +                   FWCfgReadCallback fw_callback, void *callback_opaque,
> +                   bool extendable);
>  int rom_add_elf_program(const char *name, void *data, size_t datasize,
>                          size_t romsize, hwaddr addr);
>  int rom_load_all(void);
> @@ -70,7 +71,7 @@ void do_info_roms(Monitor *mon, const QDict *qdict);
>  #define rom_add_file_fixed(_f, _a, _i)          \
>      rom_add_file(_f, NULL, _a, _i, false)
>  #define rom_add_blob_fixed(_f, _b, _l, _a)      \
> -    rom_add_blob(_f, _b, _l, _a, NULL, NULL, NULL)
> +    rom_add_blob(_f, _b, _l, _a, NULL, NULL, NULL, false)
>  
>  #define PC_ROM_MIN_VGA     0xc0000
>  #define PC_ROM_MIN_OPTION  0xc8000
> -- 
> 1.8.3.1
> 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK